Effects Of Mineral Ion Modified Biochar On Organic Carbon Mineralization In Coastal Wetland Soils

Biochar(BC),one of a carbon-rich material with highly aromatic structure,has been evidenced as an effective material to enhance the soil capacity of carbon sequestration.However,BC is usually characterized by high heterogeneity in its properties,which are higly determined by the raw material and pyrolysis conditions.This may result in the high uncertainties in the stability of BC and its impact on the mineralization of native soil organic carbon(SOC)when BC is added into the soils.In previous studies,the soil endogenous minerals have been evidenced that they can play a positive role in enhancing BC stability and inhibiting native SOC mineralization by mediating the interaction between BC and soil organic matter.Therefore,selecting mineral-rich BC(e.g.,mineral ion modified biochar)could potentially enhance SOC stability through introducing the exogenous minerals.However,the effect of mineral ion modified biochars on SOC mineralization,especially for those applied into the coastal wetland soil,is still unclear.In the present study,using reed straw as the raw material,a series of pristine biochars and mineral ion modified biochars were produced at different pyrolytic temperature(300? and 500?).A 90 d soil incubation experiment of a coastal wetland soil,which was sampled from Jiaozhou Bay wetland,incubated with different organic mattters was conducted to explore the effects of different organic additives on SOC mineralization.Furthermore,basing on the investigations on the dynamic changes in SOC mineralization,and the changes in the properties of soil aggregate and microbial community,the underlying mechanisms in related to the inhibition of SOC mineralization causing by mineral ion modified biochars addition were also illuminated.The results presented in this study could provide the scientific theoretical basis for establishing efficient and sustainable technology for remediating the “carbon sink” function of coastal wetland soil.The main research conclusions obtained in this paper are as follows:(1)Compared to pristine biochars,the physico-chemical properties of BC were significantly altered after mineral ion modifications: Mineral ion modified biochars significantly increased BC yield,ash content,and cation exchange capacity(CEC),while significantly reduced C,N,and H content,pH,specific surface area,pore volume and dissolved organic carbon content(p<0.05).Notably,the pH of ironmodified biochars(1.65?1.83)were extremely lower than those of pristine biochars.Moreover,the results also demonstrated that mineral ion modified biochars were successfully loaded with a large number of Ca or Fe minerals,which enriched the variety and quantity of surface functional groups and had a good aromatization structure.(2)The dynamic monitoring results of SOC mineralization indicated that the mineralization process of SOC could be divided into two obvious stages: the early stage of rapid mineralization and the later stage of slow mineralization.The negative priming effects on native SOC were observed for CRBC500 and all iron modified biochars due to their significant lower C mineralization levels than the control.Moreover,the observed soil organic carbon mineralization(Cm)under pristine biochars and mineral ion modified biochars were significantly lower than that under reed straw treatment,indicating that the conversion of reed straw to BC was beneficial to the improvement of SOC.(3)The measured changes in soil aggregate indices demonstrated that the percentage of water-stable macro-aggregates(>0.25 mm)and the stability of soil aggregates were significantly improved by the mineral ion modified biochars(p<0.05).Meanwhile,the distribution of total organic carbon(TOC)in 1?0.25 mm macro-aggregates was also increased in soils amended with mineral ion modified biochars(p<0.05).These results confirmed that the formation of soil water stable macro-aggregate(>0.25 mm)could be promoted by the mineral ion modified biochars,which could be attributed to their abundant contents of minerals and oxygen-containing functional groups,thus enhancing the physical protection of SOC in the macro-aggregates.(4)The measured changes in soil microbial community showed that the richness and diversity of soil microbial community were significantly decreased under mineral ion modified biochars treatments when compared with other treatments(p<0.05).Furthermore,a distinct shift of microbial community from the labile-C preferential bacterial phyla-dominant(e.g.,Proteobacteria and Bacteroidetes)to recalcitrant-C preferential bacterial phylum-dominant(e.g.,Firmicutes)community was also obsereved for iron modified biochars treatments.This change may be beneficial to a long-term sequestration of C in soil.Combined with the results of the redundancy analysis,the high stable carbon and low labile carbon(e.g.,dissolved organic carbon)input of iron modified biochars,as well as the significant reduction of soil pH,werethe important mechanisms leading to the changes in the microbial community structure mentioned above.